Derived relative motion information, which uses a dead reckoning process, is subject to cumulative error. Thus a tracking system relying on dead reckoning alone may have a continuous decrease in accuracy, which makes derived relative motion information not trustworthy over long periods of time. Many other aiding sensors have been considered including ranging and optical based mapping systems.
The user track and map information that is acquired by use of multiple sensors is combined so that the map information can compensate for dead reckoning, e.g. inertial, drift while user motion/track information can allow perceptually aliased feature information to be disambiguated.